The investigators propose to study the interactions between HHV-6 and genetic elements controlling CD4 gene expression by examining: 1) which genetic elements (promoter, enhancer, silencer) are activated/derepressed by HHV-6, and 2) which HHV-6 gene(s) is(are) responsible for turning on the CD4 gene. This knowledge may shed light on the immunobiological properties of HHV-6 and how its activity may contribute to HIV disease, and it may also contribute to a more complete understanding of fundamental immunological questions such as the control of gene expression of immunocompetent cells.